1. Field of the Invention
The present invention is directed towards connection systems for communicating electrical signals, and more particularly, to a high-reliability, matched impedance, shielded-pair interconnection system adapted for high speed data transmission up to and exceeding one gigabit per second for protocols such as Ethernet, 1394, USB, 1553, Fibre Channel, VME, Can-Buss, J1708, and the like.
2. Description of Related Art
With the increasing demand and complexity of modern electronic systems in high reliability applications such as military and aerospace, there is a continuing need to incorporate more electronic equipment into a confined space, while at the same time ensuring reliability in harsh environments. In such applications, connection systems provide a critical communication link between physically separated electronic devices. These connection systems have to satisfy many competing requirements. They should be capable of withstanding a rugged environment that includes vibration, wide temperature swings, moisture, and exposure to hazardous materials and chemical contaminants. They should also be compact to permit many interconnections to be made within a small area. And, they should have the highest quality electrical characteristics, with matched impedance, very low signal loss, and minimal crosstalk.
High reliability connection systems are often used to facilitate 100Base T and 1000Base T Ethernet applications such as those found in commercial avionics systems. Additional applications, for example, include aircraft data networks, in-flight entertainment systems (IFE) and other mil-aero networking applications where Gigabit Ethernet IEEE 802.3, Fibre Channel XT11.2, 1394, USB, 1553, Fibre Channel, VME, Can-Buss, J1708 or other multi-gigabit connectivity architecture is required. In such communication networks in which it is desirable to transfer data at high speeds over distances up to one-hundred meters, it is known to use balanced matched impedance copper cabling. The copper cables are connected to the various interfaces in a communications network using plug-in modular connectors. A conventional cable used to transfer data includes an insulating cable sheath that contains pairs of copper wires. The wires are twisted together in order to reduce crosstalk, which is a form of signal degradation that results when the signal on one wire is inductively coupled onto another adjacent wire. The Ethernet protocol uses four pairs per channel, and each pair needs to be shielded from the other pairs to preclude cross-talk between the pairs. Furthermore, when the channel is used in a full duplex manner, i.e., to support simultaneous bidirectional communications, it is also necessary to prevent disturbance by near end crosstalk and far end crosstalk from the other pairs. Thus, in a given Ethernet channel, there are six disturbing sources per pair. Consequently, both the position of the wires and the components of the modular connector all play a crucial role in preventing signal degradation.
Two commercially known modular connectors for Ethernet applications are the RJ-45 and the Quadrax contact. The RJ-45 is an eight-wire connector used commonly to connect computers onto local-area networks (LAN), especially in building applications. The connector or jack includes a generally plastic body having eight metal contacts that connect to four pairs of wires that terminate inside the jack. To attach the RJ-45 connector to a cable, about two inches of the cable sheath is stripped off exposing the four pairs of twisted wires. Each pair is untwisted and the wires are flattened out and trimmed down to approximately one-half an inch in length. These wires are inserted into the jack and connected to the metal contacts. A device such as a crimping tool is used to press down the contacts onto the wires, thereby terminating the wires in the RJ-45 connector.
Despite the prevalence and low cost of the RJ-45 connector, it also has many limitations. One drawback is that the wires have to be untwisted in order to be inserted into the jack. By untwisting the wires, even if over a small length of cable, the wires become susceptible to signal degradation due to crosstalk. Another drawback of the RJ-45 connection is that the connector is not environmentally sealed. The wires that terminate at the end of the jack are exposed to the environment and can become damaged by fluctuating temperature conditions and contaminants resulting in a poor electrical connection. Yet another drawback is that the contacts and other components of the connector are not repairable. If there is any damage to a contact, the entire connector must be removed and replaced. For these and other reasons, the RJ-45 does not meet military and aerospace specifications (Mil-DTL-38999, which has a Mil-STD-1560 insert performance requirement). Moreover, the contacts are not designed to meet vibration and shock requirements set out by these specifications. Furthermore, some wire designs require maintaining a matched impedance parallel geometry.
In lieu of the RJ-45, the Quadrax contact is used for many military or other high-reliability applications. Quadrax contacts are a multi-signal contact system employing two pairs for use with quad-axial cables. The contacts feature a one-piece dielectric design that helps simplify the termination process. The Quadrax contact has a cylindrical metal shell that is swaged to the braid of wires over a crimp support sleeve. The shell encloses four inner contacts that are intended to connect to two pairs of wires. Thus, two Quadrax contacts are required in order to connect four pairs of wires or one gigabit Ethernet cable. The two Quadrax contacts are contained in a size 17 shell, having an outside diameter of 1.415 inches, which is very bulky. The Quadrax contacts provide a significant improvement over the RJ-45 in terms of ruggedness and cross-talk reduction, but are not without other disadvantages. Even though the four pins are shielded overall, each pair is not shielded from the other. Additionally, the pins are prone to bending. Like the RJ-45, the inner contacts of the Quadrax contact are not repairable. Replacing the contacts requires cutting through the outer contact, which makes the assembly on the inner contacts non-repairable. Thus, the entire Quadrax contact needs to be replaced if there is any damage to the inner contacts.
For each of the foregoing reasons, a need exists for an improved matched impedance, shielded-pair interconnection system for high speed data transmission up to and exceeding one gigabit per second for harsh operating environments